Recently, the importance of an immunoassay by immunochromatography which does not require the pretreatment of an analyte as a simple in vitro diagnostic kit or a portable diagnostic device for detecting an antigen in a sample solution utilizing a specific reactivity of an antibody has been increasing. In particular, a test kit for a pathogen such as a virus or a bacterium is an immunochromatography device which is familiar and widely used also in an ordinary hospital and clinic.
The simplest structure of the immunochromatography device is a structure in which a sample addition part, a labeling substance retaining part, a chromatography medium having a detection part supported thereon, and an absorption part are mutually connected to each other.
Among these, for the absorption part, cotton, a non-woven material, a filter paper, or the like composed of cellulose fiber, pulp fiber, or the like has been conventionally used. However, an absorption material composed only of such a material has a poor ability to retain a developed component which has been once absorbed, and as a result, there is a problem that the backward flow of the developed component from the absorption material occurs.
Conventionally, in order to prevent such backward flow of the developed component from the absorption material, an attempt that the absorption material is formed using high water-absorbing fiber has been made (PTL 1). Further, an absorption material containing a water-absorbing polymer has been proposed (PTL 2).